Intermediary complex

According to Sapunov et al.224,2261 the following intermediary complex is formed in the reaction of phthalic anhydride with various alkanols ... 

Both for reaction in and IV the order with respect to catalyst is 0.5. The activation enthalpies are 96.6 3.4 and 97.6 3.4 kJ mol-1 respectively when Ti(OBu)4 is used as the catalyst. This is not too far from the activation enthalpies200 for the Sn(II)-cata-lyzed esterification of B with isophthalic acid (85.1 4.9) and with 2-hydroxyethyl hydrogen isophthalate (85.8 4.2). It is also close to the Ti(OBu)4-catalyzed esterification of benzoic acid with B (85.8 2.5)49. This is probably due to the formation of analogous intermediate complexes and similar catalytic mechanisms. On the other hand, the activation entropies of reactions III and IV are less negative than those of the reaction of benzoic or isophthalic acid with B. This probably corresponds to a stronger desolvation when the intermediary complex is formed and could be due to the presence of the sodium sulfonate group. 

The configuration of the product in diastereoselective hydrogenation -whether 1,2-syn or 1,2-anti - is related to the substitution pattern of the starting alkene. The allyl alcohol with a 1,1-disubstituted olefin unit affords the antiproduct, while the syn-product is formed from the allyl alcohol with a trisubsti-tuted olefmic bond (Table 21.8, entries 6-9). The complementarity in diastereoselective hydrogenation of di- and tri-substituted olefins may be rationalized based on the conformation analysis of the intermediary complex (Scheme 21.1)... 

In entries 10-13 (Table 21.8) of trisubstituted alkenes, very high diastereo-selectivity is realized by the use of a cationic rhodium catalyst under high hydrogen pressure, and the 1,3-syn- or 1,3-anti-configuration naturally corresponds to the ( )- or (Z)-geometry of the trisubstituted olefin unit [48, 49]. The facial selectivity is rationalized to be controlled by the A(l,3)-allylic strain at the intermediary complex stage (Scheme 21.2) [48]. 

The results presented in Scheme 9.5 and the results with (Zj-substrates (cf Scheme 9.3) clearly demonstrate that the Ir-catalyzed reactions involve intermediary nonsymmetric 7i- or o-allyl-Ir-complexes. The intermediary complexes undergo slow racemization (or epimerization) via o-rr-o-rearrangement or sigma tropic 1,3-rearrangement (Scheme 9.6). Evans and Nelson have proposed 7i/o- or myl-complexes as intermediates of analogous Rh-catalyzed reactions [13]. Whether the... 

Figure 4 in Scheme 2.3-2 reveals that with comparable and Pt-intermediary complexes, differences in local symmetries may result. In addition, Ni promotes interactions with a primary carbon atom of the a-allyl group whereas Pt interacts with the substituted carbon atom of this group. 

Isolation of Intermediary Complex. We believe that we were successful in isolating the intermediary complex formed during the induction period. Again we concentrated our attention on the system TMPD-bis(N-butylsalicylaldimino)cobalt(II) and for this isolation 40°C. was found... 

The intermediary complex in the system TMPD/bis( N-butylsalicyl-aldimino) cobalt (II) is assumed to be an inactive bidentate chelate... 

We thank A. J. Owen for carrying out the thermal decomposition of the intermediary complex. The technical assistance of Jean M. Burgess, D. Thompson, and the late P. Flood in various parts of the work is gratefully acknowledged. 

It should be noted that majority of the available data for processes discussed in Sects. 19.2 and 19.3 are pertinent to the light H/H2 isotopes of hydrogen. In a D-T fusion reactor plasma, the processes enumerated in Sects. 19.2 and 19.3 will take place for D,T atoms and D2,DT and T2 molecules and their ions. The vibrational energy levels in the molecular species of heavier hydrogen isotopes are different than those in H2 this introduces differences in the corresponding cross-sections for the same types of processes (even after an appropriate mass scaling of vibrational energies). More importantly, there are certain types of molecular reactions that proceed via formation of an intermediary complex (such as (Hj/), (H, ), Hg, and... 

The following structures were suggested for the intermediary complex ... 

The characterization of the geometric aspects of a reaction mechanism (definition of the RC, geometry of TS, intermediary complexes, etc.) performed on the basis of in vacuo calculations alone is a risky strategy. It is by far safer to rely on methods giving G (R) directly. This is why we consider it advisable to use accurate continuum methods or combined QM/MM simulations, where the QM part is treated at a sufficient degree of accuracy, as the hybrid QM/MM description of the solute can give. 

Initially, reduced " Tc activity and ethylenediaminetetraacetic acid (EDTA) form an intermediary complex, which is transformed slowly by ligand exchange to the Tc(V)-ECD complex, showing high in vitro stability. Originally, glucoheptonate had been used instead of EDTA (Cheesman et al. 1988). 

Kinetic experiments with a partially purified enzyme from Ehrlich ascites cells and with recombinant protein suggest that the reaction catalyzed by alkyl-DHAP synthase involves a ping-pong mechanism, with an activated enzyme-DHAP intermediary complex playing a central role [26]. The existence of this intermediate would explain the reversibility of the reaction since the enzyme-DHAP complex can react with either fatty alcohols (forward reaction) or fatty acids (back reaction) (Fig. 4). Acyl-DHAP acylhydrolase does not... 

The steady-state kinetic treatment of multisubstrate random enzyme reactions gives rise to the forward rate equation of higher order in substrate terms that reflect the number of substrate addition in the formation of intermediary complexes. The transformations are nonlinear. For example, the steady-state treatment of the random bi bi reaction gives, in a coefficient form ... 

D Pg8Q I Q] -> D Pg8o I Q This intermediary complex could operate as an efficient non-photochemical trap by fast internal charge recombination. Since two Pheo a are located in the center (II and 1 ) and only II is involved in photoreduction of 0, we may speculate that 1, rather than II is involved in the proposed energy-dissipating complex. It requires further examination to fully understand this potentially important quenching state. 

The proposed mechanism (Scheme 11) of the asymmetric epoxidation of a-ylideneoxindoles (97) by TBHP to cis- and frani-spiro[oxirane-oxindole] derivatives (101 and 102) had TBHP react with the catalyst (5)-a,a-diphenylprolinol (95) in the initial step forming a tight ion pair (96), which attacks the Cp carbon of the substfate (97) to give a transitory intermediary complex (98) as precursor of a long-living intermediate (99) from which (101) and (102) are derived. " 0... 

Lindeke B, Paulsen-Sorman U, Hallstrom G, Khuth-ier AH, Cho AK, Kammerer RC (1982) Cytochrome P-455-nm complex formation in the metabolism of phenylalkylamines. VI. Structure—activity relationships in metabolic intermediary complex formation with a series of alpha-substituted 2-phenylethyl-... 

Burke et al. also observed the above mentioned reactivity difference. They explained it in terms of an intermediary complex (A), resulting from the formation of an intermolecular hydrogen bond in the case of the ortho reaction. For the case, this mechanism may be written as follows ... 

Siffert ef ah studied the inhibition of 8-trypsin by pure P-NO2-ZACK. The enzyme concentration was 10 /iM, inhibitor concentrations varied between 6 and 2.5 X 10 = 0.25 mM, and the pH was maintained at 7.0 at 25°. Within 10 min, activity was completely lost at an inhibitor-enzyme ratio of 17 1. The study of the saturation kinetics of inactivation showed that the line could be drawn through the origin, indicating that essentially no reversible intermediary complexes were formed. 

When optically pure aldehyde was used, stereocontrolled back-side boronation of the intermediary complex X assured formation of a,p-aminoalcohol XI in the trans relative configuration and defined the absolute configuration at the second stereogenic centre. 

Intermediary complex 2 owes its stability to strong N-Mg coordination preventing reaction with the second mole of Grignard reagent. Only on pouring of the reaction mixture into water does it hydrolyze to the targeted ketone TM la. 

Chiral bidentate 0,N-ligand (-)-DAIB, (-)-3-exo-(dimethylamino)isobomeol, efficiently catalyzes the alkylation of aldehydes when present in a 1-2 % molar ratio. The ligand coordinates diethyl-zinc in the first step and forms a dimeric complex. An intermediary complex coordinates one mol of aldehyde and decomposes into monomeric species enabling the transfer of ethyl to the carbonyl group. In the last step, chiral alcohol is eliminated, and the ligand returns to the catalytic cycle [9]. 

The usual procedure is to measure the enzyme activity when a steady state has been reached. In the steady state the intermediary complex concentration remains constant while the concentration of the substrate and end product are changing. For this state, the following is valid ... 

Cd l2] complex that occurs when Cd + and 1 ions are put together in solution must be realized through the inferior complex [CdI]+,+ which consequently must exist in solution. Indeed, the complexes that possess several identical ligands cannot be formed without involving successive steps. The calculations carried out on some analytical data concerning solutions allow the determination of the formation equilibrium constants of these intermediary complexes, even if they have not been isolated (see Chap. 24) ... 

The intermediary complex [Hg(NH3)2Cl2] is called a fusible precipitate. 

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